Tinkering with a D34 I bought and found this after the teardown. While I already decided it's getting replaced, thought I'd throw it out there and see what everyone thinks.
Technically they have lifetime warranties. IDK how to advise on an explanation to Umarex about what you found though.
If the gun isn't shooting to spec I would call them and send it in to swap for a brand new one under lifetime warranty. You probably get a free spare stock too.
It's not a new rifle, older gun shop find the owner just wanted gone. He made me an offer I couldn't refuse and I walked out with a 2002 built D34 and softside gun case for $75.